Rats & lizards

I spent the Sunday previous, as I’m sure many of you did, watching videos on fractal shapes, the creation of non-Euclidean planes from both beads and balloons as well as the mathematical process of fitting an infinite amount of quickly sketched elephants onto a sheet of 8.5×11.

Well, one thing lead to another, and I ended up reading a fascinating study by Minghong Ma, from the University of Pennsylvania School of Medicine. Ma and his team studied the mechanisms of infant bonding in rat pups and made an interesting discovery

The study found that the neurons in the nose of rat pups matured after birth, and the rats only developed an attachment or “bond” with their mother and siblings after birth — as opposed to the notion that maternal development begins in the womb.

“Using patch-clamping — a technique that measures electrical signals at the cellular level — Ma’s team found that between birth and day 30 of development, normal neurons become six times more sensitive to their sibling’s scent, in this case, a fragrance called lyra,” as reported in a Penn Medicine news release.
The finding is interesting because it locates the biological basis for a behaviour we take for granted, as it is considered so “natural.” It turns out that maternal behaviour as well as the infant bonding process is not the result of a highly developed brain and the subsequently resulting emotions.

The bond is largely due to the workings of a few proteins and hormones. A critical protein in mediating the development of the parental bond is known as the OMP or “olfactory marker protein.”

Ma’s team found that the time it took for mice to respond to a certain scent decreased with their familiarity to the scent. In other words, mothers and their pups would more quickly recall their scents than those of strangers, helping reinforce the parental bond.

To test the feasibility of this scent-based bonding system, “the team also used a novel behavioural assay to illustrate one consequence of mistakes in this cellular maturation process. Normal mouse pups, given the choice between their mother and an unrelated, lactating female will choose to huddle with or suckle their mother 78 per cent of the time. But in the absence of OMP, newborn mice fail to make that distinction.”

The study leaves off with a number of questions pertaining to the exact process of maturation of the cells and the exact method of bonding. However, this got me thinking about the nature of parental care in general, and more exactly, how far back does this behaviour go in mammals? At that moment I needed to know whether parental care was something that was unique to mammals or if it went back farther. Thankfully, Google was there to appease my sudden onset of curiosity.

After some digging, it turns out that some reptiles feature adaptations that enable them to care for their young, a finding that adds significant weight to the theories of evolutionary psychology. These behavioural adaptations allowed mammals to rise, argues professor Dave C. Bell, in a study entitled “Evolution of Parental Caregiving.” In it he lists four hypothetical cognitive-behavioural “steps” that a primitive reptile would have to take, metaphorically, to be able to “raise” their young and pave the way for the evolution of mammals.

It’s important to note that Bell draws the assumption (using behavioural models and fossil evidence) that primitive reptiles lived alone, laid eggs and did not care for their young. With that in mind, these are the four evolutionary requirements:
The development of a system that inhibited stranger rejection.

The development of a dyadic emotional preference bond (corresponding approximately to the simple proximity caregiving system identified by Bowlby, 1982).

The development of mammary glands and vivaparity (live births).

The development of a nurturant caregiving system directed toward the needs of the infant (related to, but more general than, the security caregiving system).

Most of the list is self-explanatory and makes sense in an adaptive evolutionary view. The study finds that some lizards, but not others, tolerate the presence of young. Bell finds that very early on in animal evolutionary history, a “stranger rejection” system arose in the brains of animals.

As the name implies, the system is used to identify and reject strangers — either by escape or self-defence. It works by using the hormones vasopressin and oxytocin to control “built-in” behavioural responses.

Overcoming this system, Bell argues, is the key adaptation that led to the rise of mammals. By allowing their young to remain nearby, the young of these proto-mammals (modified reptiles) gained an evolutionary advantage. Further evolution occurred in other behavioural pathways in the brain, eventually leading to the complex caregiving behaviour we find in animals such as rats. Interestingly enough, Bell’s study independently found that the same process of familiarization was present in reptiles as was in rats — the time it took for a reptile to recall a familiar smell decreased with exposure.

Perhaps with the advancement of technology and testing methods, we’ll be able to trace back other, more complex behaviours and emotions to precursor behaviours in older animal lineages. These relatively new findings fill out our understanding of the evolutionary tree and allow us to better place ourselves in relation to the other things we share the planet with.